1. Field of the Invention
The present invention relates to gas generators for inflating vehicle inflatable restraint cushions, commonly known as an air bag restraint systems, so as to provide impact protection to occupants of the vehicles. More particularly, this invention relates to an improved apparatus for the ignition of gas generating material within the inflator.
2. Description of Related Art
The part of an air bag restraint system for use in the passenger compartment of a vehicle, referred to as an air bag module, typically includes a canister, which encloses a gas generator, or as it is commonly known an inflator, and at least part of an air bag, and a cover which conceals the air bag module from view. When the vehicle is involved in a collision, a crash signal initiates operation of the inflator to cause the air bag to deploy. The inflator produces an inert gas (e.g., nitrogen) which is directed under pressure into the air bag to force the air bag out of the canister incorporated in the module and into the passenger compartment of the vehicle. In a pyrotechnic type, inflator gas is produced by the burning of a gas generating material. As the air bag is forced out of the container, pressure exerted on the cover causes selected portions of the cover to separate in a predetermined manner along tear seams to enable the air bag to be directed into the passenger compartment. As the air bag is directed into the passenger compartment, it is inflated by the continued flow of gas produced by the inflator.
The gas generator for a passenger vehicle includes a disk-shaped or a cylindrical housing having openings therein for release of gas. A gas generating material is deployed in the interior of the housing in pellet or wafer form. A cooling and filtering structure surrounds the combustible gas generating material charge in order to filter out hot or burning particles and cool the gas produced by the gas generating material. Ignition of the gas generating material is achieved by an igniter tube extending through the gas generating material along the axis of the charge and the housing. The tube typically contains a rapid detonation or deflagration cord, or fuse, and igniter powder. An electric initiator and charge, or squib, is mounted to the housing and lights the rapid deflagration cord. The rapid deflagration cord in turn sets off the igniter powder, which bursts the igniter tube and lights the gas generating material.
Typically, the energizing terminals of electric squibs are connected by parallel rod conductors to the interior of a container or cup containing a pyrotechnic material. In another form, a coaxial type, one of the conductors is tubular in form and the other conductor is a rod centrally positioned therein. The ends of the conductors in the container, in both types of electric squibs, are joined together by a resistance wire or bridge that is designed to rapidly heat the pyrotechnic material to its ignition temperature when energized with sufficient electrical current.
A long standing problem with electric squibs is that their energizing terminals tend to function as antennas that pick up extraneous radio-frequency and electro-static energy. Radar signals are of particular concern because of their tendency to form transitory peaks of high intensity that are capable of firing the squib. Such firing is caused either by heating the pyrotechnic material of the squib to its flame temperature by way of a contiguous, metallic part, or by corona discharge or sparking into the pyrotechnic material.
A solution to the problem has been proposed by Holmes, U.S. Pat. No. 4,306,499, which patent is assigned to the assignee of the present invention. Holmes discloses a pair of normally ungrounded terminals surrounded by a chamber holding ferrite beads. The ferrite beads are in thermal contact with the grounded chamber walls. The ferrite beads dissipate radio-frequency electrical energy and the heat generated thereby is conducted to the grounded walls and into a heat sink. This arrangement does not provide adequate dissipation of radio-frequency during prolonged or high energy outbursts. Further, the overall design and assembly of the inflator could be drastically simplified by the elimination of an electrically energized squib. Therefore, it is preferable to eliminate electrical initiation of an air bag inflator through conductive wires such as is used in a squib.
Lewis et al., U.S. Pat. No. 3,408,937, discloses the use of laser radiation to detonate multiple explosive devices for use in space craft. The intense radiation produced by the laser is conducted through multiple light conductors to the multiple explosive devices. The explosive devices are used to provide for the rapid separation or deployment of equipment and safety devices within the space craft.